Diamondoid heat pump system

Simple cooling cycle with piston equipped gas filled pellets. SVG

With advanced APM heat pumps systems for reaching liquid nitrogen or helium temperatures can probably be easily created. They could be made into desktop scale devices with nothing more than a power connection or more importantly integrated into nanofactories to gain more reliable mechanosynthetic operation with lower error rates.

[correction: the correct cycle is probably similar to the reverse otto cycle aka constant volume cycle]
Table of thermodynamic cycles: [1]

The air refrigeration cycle also known as Bell Coleman cycle or reverse Brayton cycle (see: heat pumps in general and "gas cycle diagram" ) is nice for diamondoid AP systems since high compression ratios are easily archivable and liquid nitrogen temperatures can be archived just by using ambient air

An easy to implement (but not optimal) gas cycle is like follows:

1. compress gas in thermal contact to the heat radiator to fluid densities (around ~1000bar)
2. let the generated compression heat dissipate into the environment
3. transport compressed gas inside through the thermal isolation layer while exchanging heat with out going gas (capsules)
4. expand gas in thermal contact to the isolated volume
5. let the now absent expansion heat be filled from the chamber (suck it cold)
6. transport expanded gas throug isolation layer while exchanging heat with the ingoing gas (capsules)
7. repeat the cycle

To reach liquid hydrogen or helium temperatures the compressed hydrogen/helium must be cooled below its inversion point or else the gas will heat up instead of cooling down when expanded. A two stage design with good thermal contact is then needed.

Gasses can be handled safely (without explosion hazard) in small small DMME capsules with lockable pistons. When oxid-ceramic diamondoid materials are used dry air instead of pure nitrogen should be safely usable.

To keep the capsules small in spite of the high compression ratios the capsules could employ three consecutively acutated pistons each compressing the enclosed gas by a factor of ten.

Since the capsules must be moved between two locations seperated by macroscopic distance the design (and the process steps) will be spread over multiple microcomponents.

The most difficult part is the thermal thermal isolation layer since diamond is pretty much the worst thermal isolator conceivable. If SiO₂ structures can be mechanosyntesized AP aereogel might be usable.